1. Field of the Invention
This invention relates to a high-pressure fuel supply control device for internal combustion engine that injects fuel into each cylinder while controlling the fuel pressure within a fuel rail at a target value, and particularly to an energy-saving high-pressure fuel supply control device that limits the time of energizing a flow rate control valve.
2. Description of the Related Art
Recently, in order to reduce exhaust gas, internal combustion engines that control the fuel pressure within a fuel rail to a high pressure and inject fuel particles have been proposed (see, for example, Patent References 1 and 2).
The configuration of a fuel system in an internal combustion engine of this type will be described hereinafter.
A high-pressure fuel pump for maintaining fuel at a high pressure has a plunger that reciprocates in a pressurizing chamber. The lower end of the plunger is pressed in contact with a pump cam provided on a cam shaft of an internal combustion engine. Thus, when the pump cam rotates as it is interlocked with the cam shaft, the plunger reciprocates in the pressurizing chamber, increasing and decreasing the capacity of the pressurizing chamber.
An ejection path on the downstream side of the pressurizing chamber is connected to a fuel rail via an ejection valve that only allows circulation of fuel moving from the pressurizing chamber toward the fuel rail. The fuel rail holds the fuel ejected from the pressurizing chamber and distributes the fuel to a fuel injection valve.
A low-pressure path on the upstream side of the pressurizing chamber is connected to a fuel tank via a normally-open flow rate control valve, a low-pressure fuel pump and low-pressure pressure regulator. The fuel drawn up to the low-pressure path from the low-pressure fuel pump is regulated to a predetermined low pressure value by the low-pressure pressure regulator. After that, the fuel is sucked into the pressurizing chamber through the open flow rate control valve during a period when the plunger moves downward from a top dead center to a bottom dead center (i.e., a period when the capacity of the pressurizing chamber increases).
Meanwhile, if the flow rate control valve is closed during a period when the plunger moves upward from the bottom dead center to the top dead center (i.e., a period when the capacity of the pressurizing chamber decreases), a maximum quantity of fuel pressurized in the pressurizing chamber is supplied to the fuel rail by the upward movement of the plunger.
Conversely, if the flow rate control valve is not closed at all during the period when the plunger moves upward from the bottom dead center to the top dead center, the fuel sucked in the pressurizing chamber is relieved to the low-pressure path and no fuel is supplied to the fuel rail.
If the flow rate control valve is closed at a certain point in the period when the plunger moves upward from the bottom dead center to the top dead center, a part of the fuel sucked in the pressurizing chamber is relieved to the low-pressure path while the plunger moves from the bottom dead to the closing position of the flow rate control valve, and the fuel left in the pressurizing chamber is pressurized and supplied to the fuel rail while the plunger moves from the closing position of the flow rate control valve to the top dead center.
In this manner, by controlling the closing of the flow rate control valve at arbitrary timing in the period when the plunger moves upward, it is possible to adjust the quantity of fuel to be supplied to the fuel rail between the maximum quantity and the minimum quantity.
Hereinafter, referring to the time chart of FIG. 14, a supplementary explanation is given with respect to the relation between the closing position of the flow rate control valve and the quantity of fuel ejection in the period when the plunger moves upward from the bottom dead center BDC to the top dead center TDC.
FIG. 14 shows the relation between, from the top, the operating position of the plunger, the energization timing for a solenoid, the open/close state of the flow rate control vale, the internal pressure in the pressurizing chamber and the closing position of the flow rate control valve, and the quantity of fuel ejection. FIG. 14 also shows an operation in the case where the closing position of the flow rate control valve is decided at a time point of TVC, as an example.
An electronic control unit (ECU) as a control unit specifies a plunger bottom dead center reaching position BDC on the basis of the detected rotating position of the internal combustion engine and decides a time point that is Tr-time after the time point of the plunger bottom dead center reaching position BDC, as a time point of target valve closing position TVC of the flow rate control valve.
To close the flow rate control valve at the time point TVC, energization start timing TON and energizing end timing TOFF for the solenoid that drives the flow rate control valve are controlled.
There is an operating lag time (hereinafter referred to as pre-energization time Tp) from the start of the energization of the solenoid until the completion of the closing of the flow rate control valve. Thus, the energization of the solenoid is started at the time point TON that precedes the time point of the target valve closing position TVC by the pre-energization time Tp. Since this pre-energization time Tp changes depending mainly on the electric energy supplied to the solenoid, the pre-energization time Tp is stored in advance in the memory of the ECU as data for each battery voltage. When actually energizing the solenoid, the pre-energization time Tp is set in accordance with the detected battery voltage. This enables accurate control of the closing position of the flow rate control valve even when the battery voltage differs.
As the pre-energization time Tp passes and after the flow rate control valve is closed at the time point of the target valve closing position TVC, the fuel in the pressurizing chamber is pressurized by the upward movement of the plunger and the fuel pressure itself in the pressurizing chamber acts as a sufficient physical energization force to close the flow rate control valve. This physical energization force to close the valve continues to the plunger top dead center TDC where reduction in the pressure in the pressurizing chamber starts. Therefore, after the flow rate control valve is close and then the pressure of the fuel in the pressurizing chamber rises to a pressure Pa or higher to act as a sufficient physical energization force to close the flow rate control valve, the closing state of the flow rate control valve can be maintained up to the plunger top dead center TDC without continuing the application of an electromagnetic force to close the valve by the energization of the solenoid.
Thus, in the conventional technique, the time (hereinafter referred to as basic energization time Tbase) from the time point when the flow rate control valve is closed until the fuel pressure itself in the pressurizing chamber rises to the pressure Pa or higher to act as a physical energization force to close the flow rate control valve is stored in advance in the memory of the ECU, and this is set as a hold energization time Th (=basic energization time Tbase). This keeps the hold energization time Th to a minimum necessary time, thereby reducing the power consumption (see Patent Reference 2).
As a result, in the period from the time point of the plunger bottom dead center BDC to the time point TVC when the closing of the flow rate control valve is completed (i.e., period Tr in FIG. 14), a part (=QR) of the fuel (=QMAX) sucked in the pressurizing chamber when the plunger moves downward is relieved to the low-pressure path through the open flow rate control valve.
On the other hand, in the period from the time point TVC where the closing of the flow rate control valve is completed to the time point of the plunger top dead center TDC (i.e., period To in FIG. 14), since the flow rate control valve has been closed, the fuel (=QMAX−QR) left in the pressurizing chamber when the flow rate control valve is closed is pressurized and supplied to the fuel rail through the ejection valve.
Meanwhile, for example, if the same position as the plunger bottom dead center BDC is defined as the target valve closing position TVC, that is, if Tr=0 is set, the flow rate control valve is closed during the entire period of the plunger upward movement, and all the fuel (=QMAX) sucked in the pressurizing chamber when the plunger moves downward is pressurized and supplied to the fuel rail as the maximum quantity of fuel ejection (=QMAX).
If the solenoid is not energized at all, the flow rate control valve is left open during the entire period of the plunger upward movement. All the fuel (=QMAX) sucked in the pressurizing chamber when the plunger moves downward is relieved to the low-pressure path, and the pressurized fuel is not supplied to the fuel rail at all. Thus, the quantity of fuel ejection is zero.
In this manner, by varying the closing position of the flow rate control valve between the plunger bottom dead center BDC and the plunger top dead center TDC, it is possible to adjust the quantity of ejected fuel to be supplied to the fuel rail between the maximum quantity (QMAX) and the minimum quantity (zero).
The ECU decides a target fuel pressure in accordance with the engine operation state such as the number of rotations of the internal combustion engine and the quantity of depression of the accelerator pedal, and performs PID calculation based on the pressure difference between the target fuel pressure and the actual fuel pressure in the fuel rail, thus finding the quantity of fuel to be supplied to the fuel rail. The ECU then decides the time (or angle) Tr from the time point of the plunger bottom dead center reaching position BDC based on the characteristics of the quantity of fuel ejection with respect to the closing position of the flow rate control valve (see FIG. 14), and controls the target valve closing position.
Next, the control operation when ejecting the maximum quantity of fuel from the high-pressure fuel pump will be described in detail with reference to a time chart drawn by solid lines in FIG. 15.
FIG. 15 is a time chart showing, from the top, a reference signal REF generated on the basis of the rotating position of the internal combustion engine, the operating position of the plunger, the energization timing for the solenoid, the open/close state of the flow rate control valve, and the internal pressure in the pressurizing chamber.
In FIG. 15, the ECU first generates the reference signal REF indicating a predetermined rotating position in the rotation phase of the internal combustion engine.
The positional relation between the position of the reference signal REF and the subsequent plunger bottom dead center reaching position BDC is stored in advance as a design value in the ECU. A time point that is later than the reference signal RED by an offset value Td equivalent to a predetermined time period (or predetermined angle) is specified as a normal plunger bottom dead center BDC reaching position (hereinafter referred to as estimated bottom dead center BDC). That is, the plunger operation indicated by a solid line in FIG. 15 is recognized as a normal plunger operating position. Therefore, when ejecting the maximum quantity of fuel, the target valve closing position TVC is decided at the same position as the estimated bottom dead center BDC (i.e., Tr=0).
The pre-energization time Tp according to the battery voltage and the hold energization time Th (=basic energization time Tbase) are set. The energization of the solenoid is started at the time point TON that precedes the time point of the target valve closing position TVC by the pre-energization time Tp. The energization of the solenoid is ended at the time point TOFF when the hold energization time Th (=Tbase) has passed from the time point of the target valve closing position TVC (i.e., time point when the internal pressure in the pressurizing chamber reaches Pa or higher).
As a result, as shown by the open/close state of the flow rate control valve indicated by a solid line, the flow rate control valve is closed at the position of the estimated bottom dead center BDC and the fuel in the pressurizing chamber is pressurized during the entire period up to the time point of the top dead center TDC reaching position. Thus, the maximum quantity of fuel is supplied to the fuel rail.
The ECU performs PID calculation based on the pressure difference between the target fuel pressure decided in accordance with the engine operating state and the actual fuel pressure in the fuel rail and performs feedback control of the target valve closing position TVC of the flow rate control valve. Therefore, when the actual fuel pressure is significantly lowered from the target fuel pressure or a similar situation occurs, the quantity of feedback correction becomes excessively large. The target valve closing position TVC may move too much toward the advance side from the estimated bottom dead center BDC and the quantity of ejection may become uncontrollable.
Thus, in the conventional technique, an advance limit value LIM (=Lbase) is provided at the same position as the estimated bottom dead center BDC to prevent the movement the target valve closing position TVC from moving over the estimated bottom dead center BDC toward the advance side (see claim 2 in Patent Reference 1).
Patent Reference 1: JP-A-2002-188545 (FIGS. 5, 9 and 11 and the description of these drawings)
Patent Reference 2: JP-A-8-303325 (FIGS. 2 to 4 and the description of these drawings)
If the positional relation between the reference signal REF and the subsequent estimated bottom dead center BDC is coincident with the preset value stored in advance in the ECU (i.e., offset value Td), there is no problem in supplying the maximum quantity of fuel from the high-pressure fuel pump to the fuel rail.
However, in the actual control device, it may be considered that, for example, the positional relation between the reference signal REF and the subsequent estimated bottom dead center BDC is deviated from the normal relation because of some variations in the members concerning the position control, including the mounting position of the cam angle sensor that detects the rotating position and the high-pressure fuel pump, the processing accuracy of the pump cam and the like. The positional relation may also be deviated as the device is used for years.
However, the conventional technique does not take particular measures to deal with such variations and therefore has a potential problem as follows.
Hereinafter, a problem in the state where the members concerning the position control vary will be described with reference to FIGS. 15 and 16.
FIGS. 15 and 16 are time charts showing, from the top, the reference signal REF generated on the basis of the rotating position of the internal combustion engine, the operating position of the plunger, the energization timing for the solenoid, the open/close sate of the flow rate control valve, and the internal pressure in the pressurizing chamber.
FIG. 15 shows two control operations, that is, control operation in the case where the plunger is operating at normal timing (solid line) and control operation in the case where the plunger has a maximum deviation toward the lag side (single-dotted chain line). FIG. 16 shows two control operations, that is, control operation in the case where the plunger is operating at normal timing (solid line) and control operation in the case where the plunger has a maximum deviation toward the advance side (double-dotted chain line).
In FIG. 15, an actual bottom dead center BDC1 in the case where the plunger operating position has a maximum deviation toward the lag side (single-dotted chain line) is reached with a lag of Trtd (toward the lag side) from a bottom dead center in the case where the plunger is operating at normal timing (solid line) (that is, estimated bottom dead center BDC).
However, the ECU, which has not detected the deviation in the plunger operating position, assumes that the plunger is at the normal operating position. Then, the ECU specifies a time point that is after the lapse of an offset value Td from the reference signal REF, as the estimated bottom dead center BDC, and sets the advance limit value LIM=Lbase at the same position as the estimated bottom dead center BDC. The ECU thus controls the target valve closing position TVC (that is, Tr=0).
Therefore, when supplying the maximum quantity of fuel ejection to the fuel rail, the target valve closing position TVC is decided at the same position as the estimated bottom dead center BDC. Then, the pre-energization time Tp and the hold energization time Th (=basic energization time Tbase) are set. The energization of the solenoid is started at a time point TON that precedes the time point of the target valve closing position TVC by the pre-energization time Tp. At a time point TOFF that is after the lapse of the hold energization time Th (=Tbase) from the time point of the target valve closing position TVC, the energization of the solenoid is ended.
However, because of the deviation in the plunger operating position, the actual bottom dead center BDC1 is reached with a lag of Trtd (toward the lag side) from the estimated bottom dead center BDC. Therefore, in the worst case, the energization of the solenoid is ended before the actual bottom dead center BDC1 is reached, as shown in the example of FIG. 15, and the basic energization time Tbase in which the solenoid should be energized after closing the valve during the upward movement of the plunger cannot be secured. The fuel may pass while the flow rate control valve is left open during the upward movement of the plunger (see the open/close operation of the flow rate control valve indicated by a single-dotted chain line in FIG. 15). As a result, the fuel sucked in the pressurizing chamber is relieved to the low-pressure path through the flow rate control valve that is left open, and the fuel is not supplied to the fuel rail. The fuel pressure in the fuel rail is deviated from the target fuel pressure, causing a problem of significant deterioration in drivability and exhaust gas.
On the other hand, in FIG. 16, an actual bottom dead center BDC2 in the case where the plunger operating position has a maximum deviation toward the advance side (double-dotted chain line) is reached earlier (toward the advance side) by Tadv from the estimated bottom dead center BDC in the case where the plunger is operating at normal timing (solid line).
However, the ECU, which has not detected the deviation in the plunger operating position, assumes that the plunger is at the normal operating position. Then, the ECU specifies a time point that is after the lapse of an offset value Td from the reference signal REF, as the estimated bottom dead center BDC, and sets the advance limit value LIM=Lbase at the same position as the estimated bottom dead center BDC. The ECU thus controls the target valve closing position TVC (that is, Tr=0).
Therefore, when supplying the maximum quantity of fuel ejection to the fuel rail, the target valve closing position TVC is decided at the same position as the estimated bottom dead center BDC. Then, the pre-energization time Tp and the hold energization time Th (=basic energization time Tbase) are set. The energization of the solenoid is started at a time point TON that precedes the time point of the target valve closing position TVC by the pre-energization time Tp. At a time point TOFF that is after the lapse of the hold energization time Th (=Tbase) from the time point of the target valve closing position TVC, the energization of the solenoid is ended.
However, because of the deviation in the plunger operating position, the actual bottom dead center BDC2 is reached earlier (toward the advance side) by Tadv from the estimated bottom dead center BDC. Therefore, the valve closing control is performed, assuming the time point that is later (toward the lag side) by Tadv from the actual bottom dead center BDC2 as the target valve closing position TVC.
As a result, in the period Tadv from the time point of the actual bottom dead center BDC2 to the time point of the target valve closing position TVC, a part of the fuel sucked in the pressurizing chamber is relieved to the low-pressure path, and only the fuel left in the pressurizing chamber at the time point of the target valve closing position TVC when the flow rate control valve is closed (i.e., fuel less than the maximum quantity of fuel ejection) is pressurized until the time point of the actual top dead center TDC2 and supplied to the fuel rail. Therefore, the fuel pressure is deviated from the target fuel pressure, causing a problem of significant deterioration in drivability and exhaust gas.